1. Field of the Invention
The present invention relates to a locking slide bar or clasp of the type used to form a stiff spine for reports, presentations, and other stacks of paper assembled and bound together.
2. Description of the Prior Art
Plastic spines or slide bars for use in gripping the binding edges of stacks of papers together, such as reports, proposals, briefs, and other stacks of documents fastened together along a common edge have been manufactured for many years. Conventional report cover grips or slide bars of this type are manufactured as extruded plastic structures of uniform cross section throughout. Conventional slide grips are formed with a pair of jaws joined together at a common base and forming an open slot or gap therebetween. The jaws are laterally elongated so as to extend the entire length of the binding edge of the stack of papers. The gap between the jaws is narrow enough so that they must be forced apart slightly to accommodate the thickness of the stack of papers. The jaws can be deflected resiliently apart to increase the width of the gap therebetween so as to receive the binding edge of the stack of papers within the gap. When the jaws are released, a clamping force is exerted by the jaws against the stack of papers as the jaws attempt to move toward each other back toward their undeformed positions.
A major problem with conventional slide grips or slide bars of this type is that the gripping force is inadequate to secure the grip on the binding edge of the stack of papers. Quite often when a user opens the report the stress of parting the papers as the pages are opened is transmitted to the slide grip as a force directed outwardly away from the binding edge of the report in a direction perpendicular thereto. As a consequence, the slide grip is pushed laterally away from the binding edge of the report and pops off of the binding of the report. This tendency is aggravated when the report has a clear, slick, glossy cover, such as a clear plastic polypropylene cover of the type frequently used as a report or presentation cover to protect the papers therewithin. The low coefficient of friction on the surface of such a plastic cover makes it extremely easy for a conventional spine gripping bar to pop off of the binding edge of a stack of bound papers.
Attempts have been made to correct this problem. For example, the otherwise conventional sliding bar report cover grip sold by the JM Company located in Hasbrouck Heights, New Jersey has a report cover gripping bar provided with a pair of opposing longitudinal ribs directed toward each other near the bases of the jaws of the grip. The concept is that the additional contact with the cover provided by the ribs will enhance the gripping force provided by the slide bar on the cover. However, this system provides no positive interlocking connection between the slide bar and the report cover so that the report cover grip still slides free from the cover when the report is opened.
The Avery Dennison Company has used a gripping report cover slide bar on which the extremities of the jaws are provided with inwardly directed hooks or tangs. A polyethylene plastic report cover is folded in half and die cut near its longitudinal center fold with a plurality of arcuate, semicircular die cuts spaced periodically along its length to create a number of tabs. The curved surfaces of the semicircular tabs are directed away from the binding center fold and toward the opposite edges of the cover and of the stack of papers encompassed therewithin. However, this system still has several problems. Because the semicircular tabs lie in the same plane as the cover sheet material from which they are cut, the hooked edges of the gripping bar will sometimes fail to engage the semicircular tabs. Also, the die cuts are through both the front and back cover of the folded polyethylene cover sheet and must be spaced quite closely to the center fold line in order to be engaged by the hooks or tangs at the extremities of the jaws of the gripping bar. There is very little structure left between the front and back die cuts adjacent the fold line. As a consequence, the material can fail at the fold line and the tabs will separate from the remaining structure of the cover as generally circular die cut punch outs.